HOESY Overhauser enhancement

For compounds that contain a limited number of fluorine atoms, heteronuclear correlation spectroscopy experiments such as F H HETCOR and 2H-19F heteronuclear Overhauser enhancement spectroscopy (HOESY) can provide considerable assistance distinguishing structural isomers and diastereomers as well as for conformational analysis. HOESY experiments have been frequently used for conformational analysis of biomolecules containing fluorine labels.18... 

NMR spectroscopy has been applied in search for molecular interactions in NADES. The existence of the hydrogen bond between the fluoride ion from choline fluoride and protons from urea was observed by using the heteronuclear Overhauser enhancement spectroscopy (HOESY) [5]. The 2D NMR spectra of 1,2-propanediol-choline chloride-water (1 1 1, molar ratio) have also revealed the strong interactions among the three components involved [35]. The formation and stability of NADES can be seriously affected by the type, the number, and the spatial orientation of the HBD/acceptor groups [18]. 

Judeinstein et al have conducted direct measurement of through-space NMR interactions that provide definitive evidence for spatial proximity of different species. Dipole-dipole interactions can be measured in principle between any NMR active nuclei with heteronuclear correlation experiments in the liquid or solid state." The dipole-dipole interactions decay quickly with the internuclear distances (r ), and are difficult to evaluate for long-range distances and even more difficult when exchange, conformation, or motion phenomena are present. However, the measurement of the nuclear Overhauser method" based on the dipole-dipole-induced crossrelaxation, was proposed to successfully measure intermolecular interactions" and the formation of ion pairs." " In agreement with recent studies, the pulsed field gradient enhanced inverse HOESY (heteronuclear Overhauser enhancement spectroscopy) sequence is usually preferred because it is more sensitive for isotope pairs H- Li and also improves the digital resolution in the H crowded spectrum." ... 

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